1. Field of the Invention:
The present invention relates generally to air-conditioners for automobiles, and more particularly to an automobile air-conditioner including a variable displacement compressor.
2. Description of the Prior Art:
One example of the automobile air-conditioners of the type concerned is disclosed in Japanese Laid-open Patent Publication No. 57-175422. The disclosed air-conditioner includes a variable displacement compressor driven by the power of an engine. The displacement of this compressor is controlled according to the cooling temperature of an evaporator. The air-conditioner also includes an acceleration sensor for detecting acceleration of the automobile to reduce the displacement of the compressor to a minimum upon detection of the acceleration, thereby lowering the engine load in the accelerated condition.
In general, the accelerating ability of the automobile falls off when the engine is started or accelerated while a part of the engine power is used for driving the compressor. Japanese Patent Laid-open Publication No. 63-90420 discloses an arrangement aimed at the prevention of a decline in accelerating ability, wherein the engine power is transmitted to the drive shaft of a compressor via an electromagnetic clutch. The electromagnetic clutch is turned off to disengage the compressor from the engine power when the automobile is accelerated. Thus, the engine power is used for the purpose of accelerating of the automobile in preference to the purpose of air-conditioning the automobile.
According to the disclosed arrangement, upon detection of an accelerating condition, the displacement of the compressor is reduced to a minimum or the operation of the compressor is stopped irrespective of the outside air temperature, the temperature in a vehicle passenger compartment or the degree or rate of acceleration. As a consequence, when the outside air temperature is relatively high or when a rapid cooling operation is desired, the discharge air temperature rises unduly, thereby deteriorating the air-conditioning feeling.
In the winter or during a change of season, the air-conditioner is driven to operate in the defrost mode using the recirculating air. During that time, if the displacement of the compressor is restricted to a minimum or the operation of the compressor is stopped, the dehumidifying ability of the air-conditioner declines. As a result, the windshield and window glasses are frosted which will induce various problems in maintaining safe driving.